Boundaries for martensitic transition of 7Li under pressure

Schaeffer, Anne Marie; Cai, Weizhao; Olejnik, Ella; Molaison, Jamie J.; Sinogeikin, Stanislav V.; Santos, A. M. dos; Deemyad, Shanti

doi:10.1038/ncomms9030

Cited by 16 publications

(32 citation statements)

References 31 publications

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“…The most stable phase for lithium at room temperature and pressure, denoted β , has the body centered cubic (bcc) structure but this phase is only slightly more stable than several other phases, namely 1. the face centered cubic ( f cc) γ phase, 2. the low temperature phase α, originally considered as hexagonal closest packed (hcp), 11 then found to be 9R, 12 and recently referred to as hR9, 13 hR3, 14 or, again, 9R. 15 3. three more phases are expected to have similar free energy at room conditions.…”

Section: Introductionmentioning

confidence: 99%

Room-Temperature Lithium Phases from Density Functional Theory

2016

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Metallic lithium is a promising electrode material for developing next generation rechargeable batteries, but it suffers from dendrite formation upon recharging. This compromises both efficiency and safety of these systems. The surface phenomena responsible for dendrite formation are difficult to characterize experimentally making it important to use Quantum Mechanics (QM) to provide the understanding needed to design improved systems. The most accurate practical level of QM for such studies is the PBE form of density functional theory (DFT.) We report here an assessment of the accuracy for PBE to predict the most stable four phases of bulk lithium. PBE predicts three phases, bcc, fcc, and hcp, to be nearly equal in stability (within 5 meV.) Including the zero point energy and enthalpy corrections at standard conditions (298 K and 1 atm) we predict bcc most stable, fcc at 0.0029 eV, hcp at 0.0036 eV, and cI16 at 0.0277 eV.Indeed their experimental free energies under ambient conditions differ only by a few meV, with bcc considered most stable. Experimentally, the fourth phase becomes stable at high pressure (> 30 − 40 GPa) and low temperature (< 200 K.) In order to use QM calculations to predict growth mechanisms, it is essential to bias the calculations by imposing the desired crystal structure in the underlying layers. We consider that this will allow QM studies of dendritic growth to be studied in conditions far from the crystalline phase due to the lower surface energy of bcc.

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Section: Introductionmentioning

confidence: 99%

Room-Temperature Lithium Phases from Density Functional Theory

2016

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“…For example, at low temperatures elemental lithium adopts a rhombohedral structure, but upon heating above ∼100 K it adopts the high-symmetry bcc structure. 113 As mentioned above, the cubic Im3m structure of H 3 S responsible for the very high T c in H 3 S is stabilized down to considerably lower pressures when anharmonic quantum nuclear zero-point motion is included. 19 Both lithium at low pressures and H 3 S-Im3m at high pressures are close to structural instabilities.…”

Section: A Glimpse Of the Futurementioning

confidence: 90%

Perspective: Role of structure prediction in materials discovery and design

Needs¹,

Pickard

2016

APL Materials

123

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Materials informatics owes much to bioinformatics and the Materials Genome Initiative has been inspired by the Human Genome Project. But there is more to bioinformatics than genomes, and the same is true for materials informatics. Here we describe the rapidly expanding role of searching for structures of materials using first-principles electronic-structure methods. Structure searching has played an important part in unraveling structures of dense hydrogen and in identifying the record-high-temperature superconducting component in hydrogen sulfide at high pressures. We suggest that first-principles structure searching has already demonstrated its ability to determine structures of a wide range of materials and that it will play a central and increasing part in materials discovery and design.

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“…Upon heating, the disordered polytype enters an fcc phase before reverting to a single crystal with the same bcc orientation as that found above 150 K (19, 21). Above 100 K, isothermal compression of lithium leads to direct transformation of bcc to fcc (2,9,22).Most theoretical studies of the P = 1 atm lithium phases to date have been limited to ground-state static lattices (T → 0 K ); some even neglect the zero-point energy computed in a harmonic approximation (23-25). As a consequence, conflicting conclusions have been reached for the low-temperature structure of lithium.…”

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confidence: 99%

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confidence: 99%

“…T he behavior of the alkali metals under pressure has been a subject of considerable interest because of the emergence of unexpected physical properties (1)(2)(3)(4)(5)(6)(7)(8)(9). Lithium presents the simplest electronic structure of a metal under ambient conditions-a model for a nearly free electron crystal, with a simple and highly symmetric body-centered cubic (bcc) structure.…”

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confidence: 99%

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Evidence from Fermi surface analysis for the low-temperature structure of lithium

Elatresh

Cai

Ashcroft

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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The low-temperature crystal structure of elemental lithium, the prototypical simple metal, is a several-decades-old problem. At 1 atm pressure and 298 K, Li forms a body-centered cubic lattice, which is common to all alkali metals. However, a low-temperature phase transition was experimentally detected to a structure initially identified as having the 9R stacking. This structure, proposed by Overhauser in 1984, has been questioned repeatedly but has not been confirmed. Here we present a theoretical analysis of the Fermi surface of lithium in several relevant structures. We demonstrate that experimental measurements of the Fermi surface based on the de Haas-van Alphen effect can be used as a diagnostic method to investigate the low-temperature phase diagram of lithium. This approach may overcome the limitations of X-ray and neutron diffraction techniques and makes possible, in principle, the determination of the lithium low-temperature structure (and that of other metals) at both ambient and high pressure. The theoretical results are compared with existing low-temperature ambient pressure experimental data, which are shown to be inconsistent with a 9R phase for the low-temperature structure of lithium.lithium | Fermi surface | de Haas-van Alphen effect | low temperature | crystal structure T he behavior of the alkali metals under pressure has been a subject of considerable interest because of the emergence of unexpected physical properties (1-9). Lithium presents the simplest electronic structure of a metal under ambient conditions-a model for a nearly free electron crystal, with a simple and highly symmetric body-centered cubic (bcc) structure. Under application of external pressure, lithium undergoes a series of structural transitions to complex low-symmetry phases (3,8,10). These structural transformations are coupled with changes of its electronic properties, leading to a deviation from simple metallic behavior, including a complex phase diagram, a dramatic change in the superconducting Tc, metal-semiconductor phase transitions, as well as an anomalous melting curve (1,4,5,(10)(11)(12)(13)(14). Despite its apparent simplicity and numerous studies, there are still many open questions regarding the properties of lithium, even at P = 1 atm.Among the outstanding questions is the structure of Li at low temperature and pressure. At 1 atm and 298 K lithium crystallizes in the bcc phase. However, upon cooling it undergoes a martensitic transformation that commences at ∼80 K. Identifying the phases involved in the martensitic transition of lithium has been a challenge since its initial discovery (15). This has been due to several factors, including relatively poor response of lithium to both X-rays and neutrons; incomplete transition to the lowest measured temperature; and dependence of the transition temperature on multiple factors such as grain size, defects, and strain. The transition was first reported by C. S. Barrett (15,16). Initial neutron scattering data by McCarthy et al. (17) identified the posttransition ...

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Boundaries for martensitic transition of 7Li under pressure

Cited by 16 publications

References 31 publications

Room-Temperature Lithium Phases from Density Functional Theory

Room-Temperature Lithium Phases from Density Functional Theory

Perspective: Role of structure prediction in materials discovery and design

Evidence from Fermi surface analysis for the low-temperature structure of lithium

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